The present invention relates to a weighing machine for weighing human bodies and the like.
In a conventional weighing machine, a strain plate is strained in a manner such that a load from a scale plate on which an object to be weighed, such as a human body, is placed is transmitted to and concentrated on one point by means of a load transmission mechanism (beam balance) that is formed of a plurality of metal plates combined with one another. The change of a resistance value of a strain gauge that is pasted on the strain plate is detected, or the change of capacitance is detected by varying the distance between two electrode plates as the strain plate is displaced, and the change is converted into load.
In the beam balance described above, metal plates are used in combination with one another in a manner such that they are set upright to stand load from the scale plate, and load transmitting metal plates for transmitting the load from the scale plate to a beam metal plate must be constructed as knife edge fittings, so that the balance normally inevitably has a great thickness of 35 mm or more. Further, knife edge portions are subjected to a very high pressure, so that they are forced to deform and wear away after repeated use, thus failing to ensure long-term reliability.
To cope with this, a technique of a thin weighing machine with simple construction and high long-term reliability is described in Publication No. WO00/06977, for example. An outline of this weighing machine will now be described with reference to FIGS. 13 and 14.
As shown in FIG. 13, a weighing machine 50 is formed in a manner such that a scale plate 51, one strain plate 52, and a base plate 53 are combined in layers. The strain plate 52 and the scale plate 51 are fixed in layers with scale plate spacers 54 between them by means of bolts and screws, and the strain plate 52 and the base plate 53 are fixed in layers with base plate spacers 55 between them by means of bolts and screws. The base plate 53 is provided with a circuit portion 56, which includes control and arithmetic circuits such as a microcomputer, a display portion 57 for displaying the result of computation, and a power source retaining portion 58, and its plane shape is optional.
Further, the scale plate 51 in the form of a plate is connected to load receiving portions 59 of the strain plate 52 by means of the scale plate spacers 54. The weighing machine 50 is configured to be a weighing machine that is formed of three flat plates and can be made very thin.
In the case where the weighing machine 50 is placed on a floor surface, leg portions 60 can be provided on a part of the strain plate 52. For example, one or more leg portions 60 provided on the strain plate 52 can be arranged in any other region(s) of outer frames 61 than regions right under fixing portions 62 to which the base plate 53 is fixed. To attain this, hollow portions 63 are formed in the base plate 53.
The strain plate 52 is formed integrally of a sensitive portion 66 including a strain gauge 65 for use as sensing means, load transmitting beams 64 connecting with the sensitive portion 66, and load receiving portions 59. An upper surface 67 of the one strain plate 52 is provided with a center groove portion 68, which includes the sensitive portion 66 and is formed extending parallel to a straight line Lxe2x80x94L that connects the respective center points C of the load receiving portions 59. A weight applied to the scale plate 51 is received dispersedly by means of the load receiving portions 59, the load is caused to act concentratedly on the sensitive portion 66 by means of the load transmitting beams 64, and strain or deformation of the sensitive portion 66 is picked up as a change of the quantity of electricity by means of the strain gauge 65.
The load applied to the weighing machine 50 of FIG. 13 acts on the strain plate 52. In a weighing machine such as a scale that measures a heavy weight, in particular, screw portions for fixing the strain plate 52 and the base plate 53 are liable to loosened by repeated loading. If the screw portions loosen, the position of the strain plate 52 relative to the base plate member is shifted, so that the way the strain plate 52 is strained changes with every measurement. In consequence, measurements of the same weight involve different ways of transmission to the strain gauge 65, inevitably causing measurement errors. Further, a shock of a fall or the like also creates gaps between the strain plate 52 and screws, so that the measurement accuracy lacks in reliability.
Another prior art is also described in Publication No. WO00/06977. In this case, a strain plate and a base plate are fixed by means of the following arrangement instead of screwing. As shown in FIG. 14, a base plate 53 is in the form of an open-topped box, a strain plate 52 is arranged in the box, and fixing members 70 for preventing vibration and displacement of the strain plate 52 are arranged between the corner portions of the strain plate 52 and a peripheral wall 69 of the base plate 53.
If sides 70a of the fixing members 70 and sides 52a of the strain plate 52 are brought intimately into contact with one another, in a weighing machine of the alternative prior art described above, however, the central portion of the strain plate 52 sinks during measurement, and the sides 52a of the strain plate 52 warp, thereby pressing the inner sides 70a of the fixing members 70. After repeated use, therefore, gaps are formed between the fixing members 70 and the strain plate 52, so that the strain plate 52 is dislocated, and the measurement may possibly be subject to dispersion, as in the case of the aforesaid screwing method. If gaps are previously provided between the fixing members 70 and the strain plate 52 to prevent this, however, the position of the strain plate 52 is finely shifted with every measurement, so that measurement errors may possibly occur. A shock of a fall or the like also creates gaps between the fixing members 70 and the strain plate 52, resulting in the same problem.
The object of the present invention is to provide a thin weighing machine of high-reliability, which stands repeated use and whose measurement accuracy is influenced little by a shock of a fall or the like.
In order to achieve the above object, a weighing machine according to an aspect of the present invention comprises a substantially flat strain plate adapted to be deformed when loaded, a sensor for detecting deformation of the strain plate, a base plate member carrying the strain plate thereon, and a scale plate member located on the upper surface of the strain plate and capable of transmitting load to the strain plate, the sides of the strain plate being held by means of elastic position regulating members, individually.
The weighing machine according to this aspect can adopt the following forms.
The strain plate has a strain-direction regulating portion for regulating the direction of a strain produced in the strain plate as the strain plate is deformed. The sensor is a strain gauge attached to the strain plate corresponding to the strain direction of the strain plate. The position regulating members hold at least the sides of the strain plate which extend at right angles to the strain direction.
The strain plate is formed with at least two sides extending at right angles to the strain direction and opposed to each other across the strain-direction regulating portion, the two sides being held by means of the position regulating members, individually. Further, the position regulating members hold a plurality of portions of the sides of the strain plate perpendicular to the strain direction. Furthermore, the position regulating members hold two portions near the opposite end portions of the sides of the strain plate perpendicular to the strain direction.
The position regulating members hold those sides of the strain plate which extend parallel to the strain direction as well as the sides of the strain plate perpendicular to the strain direction. The strain plate is formed with a plurality of sides parallel to the strain direction, the sides being held by means of the position regulating members. The position regulating members for holding the sides parallel to the strain direction hold portions near the end portions of the sides of the strain plate parallel to the strain direction.
The strain plate is formed with at least two sides extending at right angles to the strain direction and opposed to each other across the strain-direction regulating portion, and the position regulating members for holding the sides perpendicular to the strain direction hold one portion near the center of each side perpendicular to the strain direction.
Each of the position regulating members includes a fixed portion fixed to the base plate member and a contact portion formed integrally with the fixed portion and in contact with the side of the strain plate, the contact portion being made elastic by means of a slit formed between the contact portion and the fixed portion.
Each of the position regulating members is composed of a fixed portion fixed to the base plate member and an elastic portion in contact with the side of the strain plate and attached to the fixed portion.
The strain plate has two openings in symmetrical positions on the opposite sides of the strain gauge, the position regulating members holding inner walls formed in the openings.
Each of the position regulating members has a protuberance, the protuberance being in contact with the side of the strain plate.
The individual sides of the strain plate are arranged so as to be in contact with the position regulating members only.
The plane shape of the strain plate is substantially rectangular, and the position regulating members are substantially L-shaped members arranged individually near the four corners of the rectangular shape. The substantially L-shaped member is formed with a hole portion such that the L-shaped member can be fixed to the scale plate member with the hole portion fitted on a fitting member protruding substantially perpendicularly from the scale plate member.
The position regulating members for holding the sides of the strain plate perpendicular to the strain direction and the position regulating members for holding the sides of the strain plate parallel to the strain direction are formed separately from one another.
Further, a weighing machine according to another aspect of the present invention comprises a substantially flat strain plate adapted to be deformed when loaded, a sensor for detecting deformation of the strain plate, a base plate member carrying the strain plate thereon, and a scale plate member located on the upper surface of the strain plate and capable of transmitting load to the strain plate, the position of the strain plate in the planar direction being settled by means of elastic position regulating members.